Semiconductor memory units commonly include addressable memory arrays and memory circuitry, including input/output pads, sense amplifiers, decoders, and control logic are frequently formed on semiconductor material. In an effort to maximize memory storage density, memory units are often stacked into multi-chip packages (“MCPs”). Having several memory units stacked into a single package increases the storage space and reduces the overall area used by the MCP, for example, on a memory module. In some memory MCPs, one of the memory units (i.e., a “master”) receives external signals and can interface with the rest of the memory units (i.e., “slave” memories) in the MCP. In routing commands to the correct memory unit of the MCP, identifying the relative location of the memory units may be necessary.
As a result, memory unit designs utilize a variety of techniques in order to determine the relative location for differentiation between each memory unit in an MCP. By determining the relative location of each memory unit, every memory unit in the MCP may be accessed by external signals despite the lack of a direct interface with the memory units of the MCP. For example, one technique used to differentiate memory locations involves manufacturing each memory separately and hard-coding memory location information directly onto the memory unit. Each memory unit then possesses its location information during initialization of the MCP. However, this technique may be costly, in addition to being complicated and inefficient from a manufacturing standpoint. In order to simplify the process, another example technique is to use all identically manufactured memory units in an MCP arranged in a master-slave configuration. The bottom memory unit in a stacked MCP is designated the master memory unit, and each of the other memory units stacked above are designated as slave memories. The master memory unit is the only one which interfaces with both external signals and the slave memory units. The master memory unit is therefore responsible for routing all incoming and outgoing signals to and from the slaves.
The use of identically manufactured memory units in a master-slave configuration adds complexity to routing signals between the master and slaves. For increased complexity, it may be useful to have additional methods to differentiate between master and slave memory units for signal routing, which often comes at increased cost, manufacturing and operational complexity, and timing penalties. Accordingly, an efficient, fast technique for determining relative master-slave location is desirable.